The officials are urging people who have been unable to communicate by phone or other means to signal helicopters passing overhead any way they can, including sheets, mirrors, flares or signal fires.

Many communities are still cut off by flooding from a week of heavy mountain rains. Rain hampered the helicopter searches yesterday, and rescuers trekked by ground to reach some isolated homes. The surging waters have been deadly, with four people confirmed killed and two more missing and presumed dead.

Emergency officials say some 1,500 homes have been destroyed and about 17,500 have been damaged by the flooding that began in the middle of last week. More than 1,200 people have not been heard from.

After swelling to a peak of 431 entries, Boulder County's list of uncounted for persons contains 212 entries for families, couples and individuals. The list contains 326 total names, KMGH-TV reported.

Hundreds more are on a similar list in Larimer County.

Sheriff Pelle's office has confirmed three deaths within Boulder County so far. Two deaths were discovered Thursday and one was confirmed Friday after previously being reported missing.

Including the two who are presumed dead, the toll of the flooding statewide is six people.

In addition to a cost of lives, Boulder County is also dealing with loss of property and infrastructure. The City of Boulder is fielding reports from residents that water or sewage is backing up into their homes.

In most cases, the city says, the backup is groundwater and not sewage.

The flooding is spread across parts of 15 counties, stretching almost 200 miles from north to south.

In Larimer County alone, the current impact area is estimated at 1,120 square miles. Another 760 are impacted in Boulder County and 385 in Jefferson County.

An estimated 35 bridges, 100 minor structures and 100 miles of road need repair in Boulder County. Emergency managers estimate $100-150 million in damage in that county.

Statewide, 26 shelters have taken in a population of 1,872 people. Nine counties and five cities have activated Emergency Operations Centers.

Copyright 2013 Scripps Media, Inc. The Associated Press contributed to this report. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.